1. Field of the Invention
The present invention relates in general to internal combustion engines and more particularly to an intake passage of a gasoline internal combustion engine.
2. Description of the Prior Art
Various methods and techniques have been proposed in the art for variably controlling the flow or swirl of the air-fuel mixture within the combustion chamber depending upon the engine operating conditions with a view to improving the fuel consumption.
FIGS. 9 and 10 show an intake device having two intake valves 1, 2 and two intake ports 3, 4 for each engine cylinder. The intake ports 3, 4 are communicated with a collector portion of an intake manifold 5 through first and second independent branch passages 6, 7, respectively. In the second branch passage 7 there is disposed a swirl control valve 9 which is adapted to close, being actuated by an actuator 8, in response to a low-load engine operating condition.
Under a low-load engine operating condition in which the swirl control valve 9 is held closed, air-fuel mixture flows into the combustion chamber only through the first branch passage 6, thus permitting the supply of air-fuel mixture into the combustion chamber to become partial and at the same time the mixture to flow at an increased speed thereby producing a strong swirl within the combustion chamber. The combustion speed is thus increased, improving the thermal efficiency and therefore the engine performances such as the fuel consumption, etc.
Under a high-load engine operating condition in which the swirl control valve 9 is held open, air-fuel mixture is supplied into the combustion chamber through the both first and second branch passages 6, 7, thus not applying any substantial resistance to the flow of the incoming mixture and therefore increasing the charging efficiency to achieve a desired engine output. In the meantime, indicated by the reference numerals 10, 11 are two exhaust valves for each cylinder.
In this kind of intake device, with a view to accomplishing easy installation of the swirl control valve 9, a valve body or spacer 14 is utilized which is formed with two intake bores 12, 13 for each engine cylinder. The spacer 14 has disposed in one 13 of the intake bores the swirl control valve 9 and is interposed between the intake manifold 5 and the cylinder head 16 in such a manner that the intake bores 12, 13 are respectively connected to the branch passages 6, 7 and the intake ports 3, 4 to establish communication therebetween. The spacer 14 is secured at its flanges 15 to the intake manifold 5 and a cylinder head 16.
In such an intake device, the spacer 14 is made of metal so that it can be produced by an aluminum die casting or the like. For this reason, the heat of the engine coolant is efficiently transmitted to the intake manifold 5, resulting in a high temperature of the intake manifold 5 and a lowered charging efficiency.
Further, such a high temperature intake manifold 5 causes the temperature of a carburetor or fuel injector to rise just after the engine is stopped, resulting in a possibility of percolation in the fuel supply line, leading to a difficulty in re-starting of the engine.